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    <link rel='stylesheet' href='../css/common.css'>

    <title>Composed Views</title>
  </head>
  <body>
    <header>
      <details id='details-panel' open>
        <summary>Composed Views</summary>
        <p>
          Tests a scenario where views are computed from the viewer space and
          composed with a separately queried viewer pose in the main scene
          reference space. This was known to be buggy in with some implementations.

          Please note this is NOT the recommended way of using the API, but it
          provides a useful validation case for implementers.
          <a class="back" href="./">Back</a>
        </p>
      </details>
    </header>
    <main style='text-align: center;'>
      <p>Click 'Enter XR' to see content</p>
    </main>
    <script type="module">
      import {WebXRButton} from '../js/util/webxr-button.js';
      import {Scene} from '../js/render/scenes/scene.js';
      import {Renderer, createWebGLContext, RenderView} from '../js/render/core/renderer.js';
      import {Gltf2Node} from '../js/render/nodes/gltf2.js';
      import {QueryArgs} from '../js/util/query-args.js';
      import {mat4} from '../js/render/math/gl-matrix.js';

      // If requested, use the polyfill to provide support for mobile devices
      // and devices which only support WebVR.
      import WebXRPolyfill from '../js/third-party/webxr-polyfill/build/webxr-polyfill.module.js';
      if (QueryArgs.getBool('usePolyfill', true)) {
        let polyfill = new WebXRPolyfill();
      }

      // XR globals.
      let xrButton = null;
      let xrViewerSpace = null;
      let xrFloorSpace = null;

      // WebGL scene globals.
      let gl = null;
      let renderer = null;
      let scene = new Scene();
      scene.addNode(new Gltf2Node({url: '../media/gltf/cube-room/cube-room.gltf'}));
      scene.standingStats(true);

      function initXR() {
        xrButton = new WebXRButton({
          onRequestSession: onRequestSession,
          onEndSession: onEndSession
        });
        document.querySelector('header').appendChild(xrButton.domElement);

        if (navigator.xr) {
          navigator.xr.isSessionSupported('immersive-vr').then((supported) => {
            xrButton.enabled = supported;
          });
        }
      }

      function initGL() {
        if (gl)
          return;

        gl = createWebGLContext({
          xrCompatible: true
        });

        document.body.appendChild(gl.canvas);

        function onResize() {
          gl.canvas.width = gl.canvas.clientWidth * window.devicePixelRatio;
          gl.canvas.height = gl.canvas.clientHeight * window.devicePixelRatio;
        }
        window.addEventListener('resize', onResize);
        onResize();

        // Set up a non-black clear color so that we can see if something renders wrong.
        gl.clearColor(0.1, 0.2, 0.3, 1.0);

        renderer = new Renderer(gl);
        scene.setRenderer(renderer);
      }

      function onRequestSession() {
        return navigator.xr.requestSession('immersive-vr', {
            requiredFeatures: ['local-floor'],
        }).then((session) => {
          xrButton.setSession(session);
          session.isImmersive = true;
          onSessionStarted(session);
        });
      }

      async function onSessionStarted(session) {
        session.addEventListener('end', onSessionEnded);

        initGL();
        scene.inputRenderer.useProfileControllerMeshes(session);

        session.updateRenderState({ baseLayer: new XRWebGLLayer(session, gl) });

        xrViewerSpace = await session.requestReferenceSpace('viewer');
        xrFloorSpace = await session.requestReferenceSpace('local-floor');

        session.requestAnimationFrame(onXRFrame);
      }

      function onEndSession(session) {
        session.end();
      }

      function onSessionEnded(event) {
        xrButton.setSession(null);
      }

      let tmpMat = mat4.create();
      function onXRFrame(t, frame) {
        let session = frame.session;
        // Get the viewer pose in viewer space, which means the pose transform
        // should be an identity matrix and the view transforms will effectively
        // be the views offsets from the center of the viewer.
        let viewerPose = frame.getViewerPose(xrViewerSpace);

        // Also query the pose of the viewer space in the local-floor space.
        let pose = frame.getPose(xrViewerSpace, xrFloorSpace);

        session.requestAnimationFrame(onXRFrame);

        scene.updateInputSources(frame, xrFloorSpace);

        if (!viewerPose || !pose) {
          return;
        }

        scene.startFrame();

        let glLayer = session.renderState.baseLayer;
        gl.bindFramebuffer(gl.FRAMEBUFFER, glLayer.framebuffer);
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

        let renderViews = [];
        for (let view of viewerPose.views) {
          let viewport = glLayer.getViewport(view);
          gl.viewport(viewport.x, viewport.y,
                      viewport.width, viewport.height);

          // Manually combine the viewer's transform with the transform of the
          // individual view to get a matrix that represents the fully composed
          // transform.
          mat4.multiply(tmpMat, pose.transform.matrix, view.transform.matrix);
          mat4.invert(tmpMat, tmpMat);
          renderViews.push(new RenderView(view.projectionMatrix, tmpMat, viewport, view.eye));
        }
        scene.drawViewArray(renderViews);

        scene.endFrame();
      }

      // Start the XR application.
      initXR();
    </script>
  </body>
</html>
